2IO NEW YORK STATE MUSEUM 



oldest thecae seem to have become completely buried in the thick peri- 

 dermal layers [see pi. 12, fig. 14 at a]. 1 



The thinner branches, on the other hand, exhibit at their surface the 

 normal transverse growth lines [see pi. 12, fig. 13]. 



The branches of T . t y p u s have not shown any trace of the presence 

 of several thecal tubes at the same level of the branch or of the existence 

 of thecae with different functions. It is, however, possible that such never- 

 theless existed within the simple tubes now alone visible and that they were 

 separated by walls of such thinness that these are not observed in the com- 

 pressed material. Perhaps the presence on several specimens [see pi. 12, 

 fig. 10-12] of strong nodes having the appearance of joint knots to whose 

 nature the writer has not been able to find any clue, will some day be 

 connected with a function of the thecae different from the purely nutritive 

 one, possibly a reproductive (gonothecal) one. The nodes appear to be 

 more or less spherical swellings of the apertural portions of some of the 

 thecae, for they show a large, round aperture. On the other hand they 

 are irregularly distributed along the stems and may have been of merely 

 parasitic origin. 



The specimens from the Upper Arenig of St Davids, Wales, identified 

 by Hopkinson and Lapworth with Emmons's species, are probably not cor- 

 rectly placed, notwithstanding their extreme general similarity to " X e m a - 

 graptus capillar is," for they are described as consisting of several 

 principal branches diverging in approximately opposite directions from a 

 central point. 



MASTIGOQRAPTUS WI1. llOV. 



o 



Hall described his genus Dendrograptus as characterized by " a broad 

 spreading shrublike frond" and by cellules, that appear "sometimes as 



1 ft must have been such thickened stipes which Gurley had before him when he 

 described the thecae of T. barrandii [1896, p. 88] as follows: "A single specimen shows, 

 scalariform-wise, the thecal mouth openings. They occupy about two thirds the width of 

 the stem and are in the proportion of 25 to 25 mm. The aspect of the stem seems to 

 oppose the view that the thecae project as in other genera from a coenosarcal canal. They 

 appear rather to have been excavated out of the substance of the branch." 



